Variable choke assembly

Abstract

A pressure reducing apparatus for controlling the pressure of oil is provided. The apparatus has ceramic components that resist wear caused by sand and debris in the oil. In one embodiment of the invention, the apparatus has a hollow body having an upstream channel, a downstream channel, and a pressure reducing chamber between the upstream channel and the downstream channel. The pressure reducing chamber has a longitudinal axis and contains a disk that is rotatable on the longitudinal axis of the pressure reducing chamber. The disk has a sidewall that abuts the upstream channel and a bottom end that abuts the downstream channel. The sidewall has a height that varies along the circumference of the disk. The disk is rotatable within the pressure reducing chamber so that the height of the sidewall facing the upstream channel can be varied to throttle the flow of oil from the upstream channel.

I claim:  
     
         1 . A pressure reducing assembly for a high pressure oil well, comprising: 
 A. an upstream channel;    B. a hollow housing having a port that fluidly connects the housing with the upstream channel;    C. a disk disposed in the housing and rotatable between a first orientation in which the port is substantially obstructed by the disk and a second orientation in which the port is substantially unobstructed by the disk; and    D. a downstream channel,    wherein the disk has a side wall that covers the port when the disk is rotated to the first orientation to substantially prevent fluid in the upstream channel from entering the housing.    
     
     
         2 . The pressure reducing assembly of  claim 1 , wherein the disk is mounted on a shaft that extends outside the housing and is operable to rotate the disk between the first orientation and the second orientation.  
     
     
         3 . The pressure reducing assembly of  claim 1 , wherein the disk is formed of a ceramic material.  
     
     
         4 . The pressure reducing assembly of  claim 3 , wherein the disk is formed of a technical ceramic material selected from the group consisting of alumina, chromium oxide, titania, zirconia, partially stabilized zirconia, silicon nitride, silicon carbide, and combinations thereof.  
     
     
         5 . The pressure reducing assembly of  claim 1 , wherein the disk comprises a cylindrical body having a radially relieved recess configured to align with the port and permit the flow of fluid from the upstream channel into the housing when the disk is rotated from the first orientation to the second orientation.  
     
     
         6 . A pressure reducing assembly for a high pressure oil well, comprising: 
 A. a hollow body having an upstream channel and a downstream channel;    B. a flow channel between the upstream channel and the downstream channel, said flow channel having a longitudinal axis; and    C. a disk having a bottom edge and disposed in the flow channel, said disk being rotatable in a fixed position on the longitudinal axis of the flow channel to alter the pressure of fluid passing through the flow channel,    wherein the disk comprises a recess along the bottom edge of the disk that aligns with the upstream channel, said recess having a transverse cross-sectional area smaller that the cross-sectional area of the upstream channel so as to form a flow constriction that reduces the pressure of fluid as it passes through the flow chamber.    
     
     
         7 . The pressure reducing assembly of  claim 6 , wherein the recess has a cross-sectional area that increases gradually to form a generally helical bottom edge, such that rotation of the disk changes the size of the flow constriction formed by the alignment between the upstream channel and the recess.  
     
     
         8 . The pressure reducing assembly of  claim 6 , wherein the disk is formed of a ceramic material.  
     
     
         9 . The pressure reducing assembly of  claim 8 , wherein the disk is formed of a technical ceramic material selected from the group consisting of alumina, chromium oxide, titania, zirconia, partially stabilized zirconia, silicon nitride, silicon carbide, and combinations thereof.  
     
     
         10 . A pressure reducing assembly for a high pressure oil well, comprising: 
 a housing formed of a metallic material, said housing including an upstream channel, a downstream channel, and a pressure reducing chamber disposed between said upstream and downstream channels;    an inlet port for permitting fluid communication between said upstream channel and said pressure reducing chamber;    an outlet port for permitting fluid communication between said pressure reducing chamber and said downstream channel;    a disk disposed in said pressure reducing chamber, said disk having a sidewall that abuts said inlet port and a bottom end that abuts said outlet port, said disk being formed such that the height of the sidewall varies from a maximum height to a minimum height around the circumference of said disk; and    means for rotating said disk within the pressure reducing chamber such that the height of the sidewall facing said inlet port can be varied, whereby oil flow through the pressure reducing assembly can be throttled.    
     
     
         11 . The pressure reducing assembly of  claim 10  wherein the bottom end of said disk comprises a helical surface.  
     
     
         12 . The pressure reducing assembly of  claim 11  wherein the bottom end of said disk further comprises a planar surface disposed at an angular position where the height of the sidewall is a maximum.  
     
     
         13 . The pressure reducing assembly of  claim 12  wherein said helical surface begins at said planar surface and terminates at a preselected distance from the plane of said planar surface.  
     
     
         14 . The pressure reducing assembly of  claim 10 , wherein the disk is formed of a ceramic material.  
     
     
         15 . The pressure reducing assembly of  claim 14 , wherein the disk is formed of a technical ceramic material selected from the group consisting of alumina, chromium oxide, titania, zirconia, partially stabilized zirconia, silicon nitride, silicon carbide, and combinations thereof.  
     
     
         16 . A pressure reducing assembly for a high pressure oil well, comprising: 
 a housing formed of a metallic material, said housing including an upstream channel, a downstream channel, and a pressure reducing chamber disposed between said upstream and downstream channels;    an inlet port between said upstream channel and said pressure reducing chamber for permitting fluid communication between said upstream channel and said pressure reducing chamber;    an outlet port between said pressure reducing chamber and said downstream channel for permitting fluid communication between said pressure reducing chamber and said downstream channel;    a disk disposed in said pressure reducing chamber, said disk having a sidewall and a bottom end, said disk having a passageway formed therein between the sidewall and the bottom end, said passageway having a first aperture in the sidewall and a second aperture in the bottom end;    means for rotating said disk within the pressure reducing chamber such that the first aperture can be moved into or out of alignment with said inlet port, whereby oil flow through the pressure reducing assembly can be throttled.    
     
     
         17 . The pressure reducing assembly of  claim 16  wherein the bottom end of said disk comprises a helical surface.  
     
     
         18 . The pressure reducing assembly of  claim 17  wherein the bottom-end of said disk further comprises a planar surface disposed at an angular position where the height of the sidewall is a maximum.  
     
     
         19 . The pressure reducing assembly of  claim 18  wherein said helical surface begins at said planar surface and terminates at a preselected distance from the plane of said planar surface.  
     
     
         20 . The pressure reducing assembly of  claim 16 , wherein the disk is formed of a ceramic material.  
     
     
         21 . The pressure reducing assembly of  claim 20 , wherein the disk is formed of a technical ceramic material selected from the group consisting of alumina, chromium oxide, titania, zirconia, partially stabilized zirconia, silicon nitride, silicon carbide, and combinations thereof.